Subtracting tens such as (80 - 20 = 60) is like subtracting quantities of
items. In this case 2 tens are subtracted from 8 tens to leave 6
tens. This is similar to 2 oranges being subtracted from 8 oranges to
leave 6 oranges.

Each digit of a number in our number system has a different place value. When
subtracting numbers, always subtract in the same place value column such as the
ones', tens' or hundreds' place values.